EWT - Steel Digester Covers
Ovivo provides a variety of EWT steel digester covers digester covers. Each digester cover is constructed as a dome-shaped segment of a sphere, offering maximum strength and structural integrity. Ovivo offers the Type F cover (fixed), frequently used as the primary of first stage digester in a two stage system and the Type GV (gasholder) which provides storage capacity for plants that desire to utilize their excess biogas for environmentally friendly electricity generation or the heating of buildings in addition to the typical heating of the undigested sludge by a dual fuel boiler.
Ovivo’s patented HydroSeal gasholder cover provides complete gas containment in normal operation and reduces digester maintenance. Because the side skirt, guides and ballast members are located in a “clean” liquid seal.
As part of what Ovivo offers, we specialize in the design and supply of Anaerobic Digestion equipment used in the treatment of municipal and industrial wastewater (including waste to energy projects). The Anaerobic Digestion products include, covers for containing the methane (steel fixed covers, steel gasholder covers, and membrane gasholder covers), sludge mixers to increase VS Destruction and methane production (including draft tube mixers and the LM mixer), and the Sonolyzer sludge disintegrating equipment. All of the products provided are recognized and used around the world.
The steel digester covers are radial beam designed to be erected quickly and efficiently, this is a simple, rigged structural design. The thrust ring is installed at the periphery of each cover to absorb all design loads without transmitting excessive forces to the concrete digester wall. During erection, the cover is supported by radial beams attached to a center ring and the thrust ring which add strength to the complete unit.
The digester cover design is compatible with all our available mixing systems. Also, a variety of accessories are available with fixed and gasholder digester covers to effectively interface with the customer’s design.
The required number of arched radial beams, side-sheet sections and cover plates varies with the tank diameter.
The Type F fixed digester cover is a simple and economical option for primary digesters. The fixed covers are supported from structural tubes resting on top of the tank wall. The entire liquid surface beneath a fixed cover is open and can be agitated by a digester mixing system. This is a key element in preventing scum accumulation on the liquid surface of the digester.
The Type GV gasholder digester cover uses the radial beam design with added side-sheet and ballast for digester gas storage. Submerge ballast blocks are used to maximize cover stability and maintain adequate gas pressure. The vertical guides are attached to the tank wall. Guide devices, spanning from the top to the bottom of the cover side-sheet, are engaged to stabilize the cover and protect the cover from substantial wind loads.
The HydroSeal design includes a separate launder and “clean” seal liquid with no annular gap. Rag and sediment accumulation on guide and ballast surfaces is eliminated and in most designs, ballast members remain easily accessible for operating pressure adjustment.
- Faster, easier installation than that offered with other designs
- Simple Construction – Low capital and installation cost
- Self supporting dome without columns, without trusses to paint or protect
- Easy to insulate
- The Type F fixed covers can be sealed against the tank wall – combats odors and foaming
- The Type GV gasholder design allows digester by-product (methane gas) to be used for environmentally friendly power generation
- The gasholder cover is design to move vertically allowing large liquid level variation.
- The HydroSeal gasholder cover provides 100% gas containment – effective odor and VOC emissions control.